Monodispersed inorganic mesoscopic structures with well-defined size, shape, chemical composition, and crystallinity, such as nanospheres, nanorods (i.e., nanowires) and nanocubes, have attracted extensive synthetic attention as a result of their novel morphology-dependent properties, which are different from that of the bulk (Xia et al., Adv. Mater., 2003, 15:353; Patzke et al., Angew. Chem. Int. Ed., 2002, 41:2446; Rao et al., Dalton Trans., 2003, 1; Alivisatos, A. P., Science, 1996, 271, 933; Cui et al., Science, 2001, 291, 851; Sun et al., Science, 2002, 298, 2176; Ahmadi et al., Science, 1996, 272, 1924).
Among the various classes of nanostructures, nanocubes have recently generated interest as potential building blocks in nanodevices, nanosensors, and functional nanomaterials. For example, a variety of nanocubes, such as metallic Ag/Au, zerovalent Fe, photoluminescent In(OH)3/In2O3, narrow band-gap semiconducting Ag2S, p-type semiconducting Cu2O, luminescent CaF2, and magnetic p-type semiconducting Co3O4, have been successfully synthesized primarily through solution-mediated reactions (Lim et al., Angew. Chem. Int. Ed., 2004, 43, 5685; Gou et al., J. Mater. Chem., 2004, 14, 735; Yu et al., J. Am. Chem. Soc., 2004, 126, 13200; Xu et al., Langmuir, 2004, 20, 9780).
By analogy, the production of magnetic materials at the nanoscale promises to be significant for technologies involving data storage density, quantum computing, spintronics, and technologies involving memory and sensor development (H. Schmid, Ferroelectrics, 1999, 221:9; Fiebig et al., Nature, 2002, 419:818).
For example, BiFeO3 shows ferroelectricity with a high Curie temperature (TC) of ˜1103 K, and antiferromagnetic properties below a Neél temperature (TN) of 643 K (Wang et al., Science, 2003, 299, 1719). Ferroelectricity is an electrical phenomenon whereby certain ionic crystals may exhibit a spontaneous dipole moment. Structural analysis of BiFeO3 indicates that it possesses a rhombohedrally distorted perovskite structure with R3c symmetry (a=b=c=5.63 Å, α=β=γ=59.4°) at room temperature (Kubel et al., Acta Crystallogr. B, 1990, 46, 698).
Also, because of their high sensitivity to ethanol and acetone vapors, bismuth ferrites have been recently considered as new materials for semiconductor gas sensors (Poghossian et al., Sens. Actuators B, 1991, 4, 545). In particular, the catalytic potential of Bi2Fe4O9 for ammonia oxidation to NO is of current interest as these iron-based materials may likely replace current, irrecoverable, and costly catalysts based on platinum, rhodium, and palladium (Zakharchenko et al. Kinet. Catal., 2002, 43, 95. and Xiong et al., Chem. Lett., 2004, 33, 502).
Despite the evident importance of Bi2Fe4O9 as a functional material, many obstacles for creating nanoscale structural motifs of this bismuth ferrite have arisen (Xiong et al., Chem. Lett., 2004, 33, 502).
For example, in its bulk form, measurement of ferroelectric and transport properties in bismuth ferrite has been limited by leakage problems, likely due to low resistivity, defects, and non-stoichiometry issues. To address this problem, recent approaches have focused on developing novel structures of BiFeO3 (Li et al, Mat. Res. Soc. Symp. Proc., 2002, 676:Y7.7.1). For instance, thin films of BiFeO3 show enhanced physical properties such as spontaneous polarization, saturation magnetization, and a piezoelectric response, that are significantly enhanced relative to that of the bulk.
However, controllable synthesis and property evaluation of the magnetic materials has yet to be achieved. In particular, there have not been any viable or controllable syntheses of nanostructures of BiFeO3.
Moreover, to date, little if any effort has been expended in research associated with the synthesis of substrate-free nanostructures of BiFeO3. Moreover, there have not been any viable reports on their single-crystalline nanostructure analogues associated with 0-D and/or 1-D structural motifs.
The fabrication of nanostructures of magnetic materials is of fundamental importance in investigating the size correlation of the basic physical properties of these materials, with implications for their device applications. Accordingly, there is a need for the fabrication of well-defined sizes and shapes of nanostructures of magnetic materials